Four-circle diffractometers D8 D9 D15 D19

The first diffractometers D8 etc were controlled by the Telemecanique CARINE system which swapped out inactive programs (running each instrument) during inactive periods. Because of the use of Fortran language for the control the instruments benefited from having a complete crystal package to orient and scan the crystal in the 4-circle goiniometer mount. The major drawback was the necessity to share the two CARINE computers between the demanding instruments. The standard chi-circles were large enough for cryogenic devices to be mounted. The single detector required the crystal to be moved to complete the measurement of the intensity of each reflection. D8 was used for refinement of crystal structures. D9, with a wider range of wavelengths on a hot source was intended for anomalous dispersion measurements to offer additional phasing information. A multidetector (8 degrees by 120 degrees) was built during upgrades, and D8 was replaced by the new D19 with this new detector. This only improved count rates by about a factor of four; it was difficult to treat incomplete data arising at the edges of the detector and the background was higher with no collimation in front of the detector.. A major software investment was made to treat the multidetector data which was amortised over the next years as larger surface area and multiple area detectors were introduced. D15 was a Harwell Mark VI diffractometer on an inclined hole. This necessarily introduced collimation in both horizontal and vertical directions. While a long distance from the core this gave it high resolution characteristics.

Polarised Neutrons D3,D5.

D3 was a modified Mark VI diffractometer designed at Harwell and delivered to the ILL when the British joined. The monochromator was initially Co-Fe, later Heusler alloy. This resolved some problems of the intense activation of the cobalt in the thermal beam. It used a PDP11 for control. D5 was a three axis instrument on a hot source beam with the possibility of polariation analysis. It was based on Brookhaven instruments and used a heavy base arm (MAN) moving about the monochromator drum. the sample crystal and secondary spectrometer were mounted.on this base. Fe-Co monochromator and analyser crystals were used.

As part of the upgrade program which included polarisation analysis being added to the IN2 three-axis instrument (becoming IN20) D5 was pensioned off, and D3 moved to the hot source beam tube.

Spin-flip analysis was achieved using radio-frequency flipping coils along the incident and final beam paths about the sample crystal.

D12

This instrument used photographic recording of a scintillator for a Laue diffractometer (white-beam) on a thermal guide. While initially used for crystal alignment it benefited from the introduction of radial collimators about the sample crystal, which lead to massive reduction of unwanted background (Wright). Subsequently suchs radial collimators were introduced on a number of instruments, including time of flight spectrometers like IN6.